The situation of the OP sounds like a bad monitor.
To mb8764, have you tried installing the drivers and software for the LG monitor or are you using the "plug and play" drivers that windows picks in the new hardware wizard? Try the LG drivers and the software if you havn't already.
I had a similar problem. It started after my old Dell CRT monitor gave out and I got a flat screen LG HD monitor. It would go to sleep, and not come back. No key would bring it back. The Num lock and Caps Lock both worked from key input. The hard drive would run, but the only thing that would bring the monitor back was a reboot.
Dell Dimension 4600 P4 2.8ghz
Nvidia Geforce FX 5200 (Dell Card)
LG W2361(analog) Monitor
Windows XP Pro. Reinstall from a non-Dell windows disk.
Video card drivers from windows or found online instead of from Dell
I reinstalled drivers from Dell for this card after a crash and error notices that I had incompatible drivers. This helped with other things but did not stop the monitor shut downs and reboots.
I did not try replacing the system (BIOS) battery. Sometimes that helps in situations like this.
I shut off all screen saver power functions to never (turn off monitor, turn off disk drives, and system standby), but it would still shut down after several hours.
I finally sat down and researched it and experimented a bit.
1) I installed the monitor drivers that came with the LG monitor. I was previously using just the display “plug and play” drivers from Microsoft that it picked automaticly.
2) I also installed the ForteManager software that came with the LG.
This fixed the problem completely.
It wakes up just fine now from all screen saver power modes (screen saver, not really a power saver mode, monitor shut down, disk drive shut down, and stand by system). Works like it is supposed to.